I'm retired now, but I'm also ADD. Didn't find out until 2002 that I was ADD. Luckily I had a family physician who spotted the signs in me. When I was in high school and college, hardly anybody knew what it was.
Also, do you have any other conditions (such as diabetes)? You say you feel like it's getting worse. Talk to your doctor, and if needed, get a complete physical. Are you married? Kids? Lots of stressors can affect your ADD.
You can function, it just takes more effort to stay focused.